This research examines the impact of chronic and acute perceptions of discrimination on psychological and physiological stress responses. Perceived discrimination is widely assumed to negatively affect both mental and physical health, but research directly addressing this issue is scarce. Drawing on models of stress and emotion, it is hypothesized thatperceiving others to be prejudiced against the self is stressful, and initiates a cascade of negative self-and other-related cognitions and emotions that in turn, initiate general physiological stress responses (e.g., blood pressure reactivity, elevated cortisol) as well as more specific stress responses associated with threat (e.g., vascular resistance) or anger (e.g., cardiac output). These physiological responses have adverse health implications if repeatedly experienced over time (McEwen, 2000). It is also predictd that resilience as well as vulnerability can occur in response to perceived discrimination. 10 experimental designs (with three replications) are proposed to assess the interrelationships among cognitive, affective, and biological (hormonal and cardiovascular) responses to acute discrimination-relevant events among Latino-Americans, African-Americans, and women. Experiment 1 tests the hypothesis that chronic or situationally induced expectations of prejudice lead to increased physiological stress responses and greater threat in evaluatively ambiguous intergroup situations. Experiments 2-4 test the independent effectsof exposure to negative social feedback and expectations of discrimination on anger and threat-related stress responses. Experiments 5 - 6 examine the physiological effects of clear rejection or selection based on social identity. Experiments 7-8 examine how a stigmatized target's situationally activated or chronically held prejudice expectations interact with the prejudice level of a nonstigmatized partner to influence stress responses in naturally occurring dyadic social interactions. Experiments 9-10 test the hypothesis that dispositional optimism and manipulated optimism increase resilience among individuals who are exposed to prejudice. All experiments assume that physiological reactions to potentially discriminatory situations are shaped by features of the situation and of the person, and test the hypothesis that negative cognitions and affective responses mediate physiological responses to discrimination-relevant stressors.